1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing the same and, more particularly, a liquid crystal display device in which a peripheral circuit or a signal processing circuit having CMOS field effect transistors is built and a method of manufacturing the same.
2. Description of the Prior Art
In the active-matrix liquid crystal display device in which the peripheral circuit or the signal processing circuit is built, the thin film transistors (TFTs) are employed in not only the display region but also the peripheral circuit or the signal processing circuit as the CMOS transistors in the analog switch and the inverter.
The low-temperature polysilicon technology is employed in the thin film transistors in the peripheral circuit or the signal processing circuit as well as the display region.
The low-temperature crystallizing technology is indispensable to the manufacture of the high-performance/low-cost peripheral driver circuit TFTs.
The typical crystallizing technology that is put currently to practical use is the low-temperature crystallizing method using the excimer laser. The thin film of the good-quality silicon crystal can be formed on the low-melting glass by using the excimer laser.
For example, the basic crystallizing method by using the excimer laser will be given as follows.
First, the amorphous silicon (a-Si) starting thin film is formed on the glass substrate by the thin film forming method such as PECVD (Plasma-Enhanced CVD), or the like. Then, in order to improve the laser resistivity of the starting thin film, the hydrogen in the a-Si starting thin film is removed by the annealing process at 400 to 450° C. Then, the polysilicon thin film is formed by irradiating the light beam of the excimer laser onto the a-Si starting thin film to crystallize. Then, the crystallinity is improved by processing the polysilicon thin film in the atmosphere of hydrogen, steam, or the like.
By using such polysilicon thin film, the switching TFT array is formed in the pixel display portion and also the semiconductor integrated circuit is formed in the peripheral circuit portion of the same substrate. Normally, the liquid crystal display device in which the peripheral circuit is built consists of the pixel display portion TFT array, the gate driver circuit, and the data driver circuit. Normally, the high-performance TFTs, which have the operating frequency in the range of several megahertz (MHz) to several tens megahertz, the field-effect mobility of 50 to 300 cm2/Vs, and the appropriate threshold voltage Vth, are employed in the data driver circuit.
In contrast, in the gate driver circuit and the pixel display portion, the request for the mobility of the TFT is not so severe. For example, the mobility of more than 20 cm2/Vs may be employed.
Meanwhile, the new technical trend of the liquid crystal display device aims at the attainment of the ultra-high definition display panel and the high-performance built-in large-scale semiconductor circuit.
First, the ultra-high definition display panel will be explained hereunder.
According to the progress of the multimedia technology and the mobile technology and the spread of the Internet, it is always required to read/process a great deal of information. For this reason, the specification requirement for the ultra-high definition displaying function is increased in the liquid crystal display device as the man-machine interface. For example, the large-size high definition display device having more than 200 dpi or the small-size ultra-high definition liquid crystal display device for the mobile device is needed in the application fields such as the multi-screen display of the homepage of the Internet, the multitask process, the CAD design, etc.
Next, the high-performance liquid crystal panel built-in type large-scale semiconductor circuit will be explained hereunder.
In the low-temperature polysilicon integral panel, there appears the technical trend that attains the intelligent panel or the sheet computer by providing the high-performance large-scale semiconductor integrated circuits in the peripheral circuit portion. For example, it is possible to build the digital driver, the data processing circuit, the memory array, the interface circuit, and the CPU in the liquid crystal display panel on the data side.
The normal thin film transistors are used as the active elements being employed in such peripheral circuit portion. As set forth in Patent Application Publication (KOKAI) 2000-36599, for example, respective thin film transistors in the peripheral circuit portion and the pixel portion are formed by the same steps, and also the wirings formed on these thin film transistors are formed by the same steps.
For instance, as shown in FIG. 1, the thin film transistor 101 in the display portion A and the thin film transistor 102 in the peripheral circuit portion B are formed simultaneously on one substrate 103, and then these thin film transistors 101, 102 are covered with the first interlayer insulating film 104. Here, the polysilicon film 100 constituting the thin film transistors 101, 102 is formed by patterning the low-temperature polysilicon film described above. The gate insulating film 110 is formed between the polysilicon film 100 and the gate electrodes 101g, 102g. In this case, the gate electrodes 101g, 102g are formed simultaneously with the first-layer wiring (not shown).
In addition, the second-layer wiring 105, the second interlayer insulating film 106, the third-layer wiring 107, and the third interlayer insulating film 108 are formed sequentially on the first interlayer insulating film 104. The second-layer wiring 105 is connected to the thin film transistors 101, 102 in the display portion A and the peripheral circuit portion B via the holes formed in the first interlayer insulating film 104 respectively. The third-layer wiring 107 is connected to the thin film transistor 102 in the peripheral circuit portion B via the hole formed in the second interlayer insulating film 106. The metal constituting the second-layer wiring 105 is employed as the black matrix BM in the display portion A. Also, the pixel electrode 109 is formed on the third interlayer insulating film 108 in the display portion A, and this pixel electrode 109 is connected to the source region of the thin film transistor 101 via the second-layer wiring 105
By the way, in the liquid crystal display panel, with the progress of the high definition display, the pixel pitch is reduced and also the peripheral circuit density is extremely increased. Therefore, the ultra high definition display panel in which the digital driver is built and which has 200 dpi or more must be formed.
For example, in the case of the 8.4 type UXGA panel, the numbers of pixels is 1600 (horizontal direction)×3×1200 (vertical direction), the display definition is 238 dpi, and the sub-pixel pitch is 35.5 μm. As another example, in the case of the 15 type QXGA panel, the numbers of pixels is 2048 (horizontal direction)×3×1536 (vertical direction), the display definition is 171 dpi, and the sub-pixel pitch is 49.5 μm.
In order to drive the pixel column of such vertical one line, the peripheral circuit consisting of hundreds to several thousands of TFTs must be installed in such narrow pixel pitch region. Also, in order to manufacture the high-performance low-temperature polysilicon intelligent panel, the sheet computer, etc., the large-scale circuits such as the digital driver, the data processing circuit, the memory array, the interface circuit, the CPU, etc. must be built in the peripheral circuit region.
However, in the multi-layered wiring structure shown in FIG. 1, even if the higher integration and the narrower wiring pitch in the peripheral circuit can be attained, the parasitic capacitance between the vertical wirings disturbs the high-speed operation in the peripheral circuit region because the wiring interval in the vertical direction is set narrower than the wiring interval in the lateral direction.